Rate circuits



Feb. 22, 1949. P. HALPERT ET AL 2,462,095

RATE CIRCUITS Original Filed Aug. 19, 1941 2 Sheets-Sheet 1 INVENTORS, RHALPERT, C.A.FRISCHE,

P. HALPERT ET AL Feb. 22, 1949.

RATE C IRCUITS 2 Sheets-Sheet 2 Original Filed Aug. 19, 1941 Patented Feb. 22, 1949 UNITED STATES PATENT OFFICE RATE CIRCUITS Original application August 19, 1941, Serial No. 407,460. Divided and this application June 27, 1942, Serial No. 448,794:

' 6 Qlairns. 1

This application is a division of copending application Serial No. 497,460, for Electrical control systems, filed August 19, 1941, now abandoned.

This'invention relates to positional control systems, for remotely controlling and accurately positioning objects such as searchlights and guns, from an accurately positioned or position-maintaining instrument. By our invention we may also control the steering of a dirigible vehicle, such as ship or airplane, by positioning the rudder or other control surface. Our invention also has application tostraight follow-up systems wherein the position of a follow-up element is accurately maintained with reference to a rotatable control or sensitive element such as a gyro compass or directional gyro.

For this purpose, we provide a novel piclz- -oif device, such as that shown in Serial No. M81340, now U. S. Patent 2,415,819, for producing an electrical signal in response to displacement of the control or sensitive element which reverses phase upon reversal of the displacement. In former pick-off devices of this type, for example that shown in Patent No. 1,959,804, to Wittlzuhns et al., issued May 22, 1934, for Non-contacting follow-up system, a useful signal is secured only through a comparatively small angle of deflection of the control element, say 1G degrees or less. W e overcome this limitation of the prior art and provide a pick-off means in which a positive signal is generated for angular deviations approaching 9% degrees. In addition, we may provide a pick-off device in which the signal output continuously increases as the deviation increases, rather than one which quickly reaches a maxi mum constant signal, as is the case in the abovementioned patent.

It has been recognized that the generation of a simple reversible signal is not sufiicient for control purposes even where such signal is proportional to the relative displacement between the position-maintaining device the controlled device. For obtaining accurate control, we pro" pose to generate an electrical signal which not only varies in phase and magnitude with the di-- rection and amount of relative displacement be tween the control and controlled device but which also varies with the relative velocity and preferably also a higher time derivative of the relative displacement. This is done by operating electrically our improved rate amplifier upon the signal obtained from our improved pick-oil means so as to add to this signal certain components representing the velocity and acceleration of the displacement of the controlling object. With this improved system, it is possible to maintain the relative displacement between two objects at practically zero, or to control the position 01 2. remote object with very high accuracy.

It is the primary object of this invention to provide a rate circuit of the above character in which the components of the rate-taking circuit are so correlated, arranged and of such adjustable character that the values of the derivative signals may be relatively adjusted. It is another object to provide a rate circuit of the foregoing character in which the magnitudes of the time derivative signals may be controlled as to their maximum values and also controlled as to their relative values. It is a still further object to provide a rate circuit of the foregoing character wherein the magnitudes of the two time-derivative signals may be simultaneously adjusted to some limiting value while the relative values thereof, as so limited, may be simultaneously adjusted.

Specifically, we employ a Ward Leonard type of control using a motor-generator set, the generator having two opposed field windings. The A.-C. reversible phase control signal obtained from our improved pick-ofi means is amplified and modified by the addition of velocity and acceleration components in our improved rate amplifier, whose output includes two direct currents which excite the opposed generator field windings to produce one or the other direction of control of the controlled object, in accordance with the phase of the pick-off signal. The controlled object may be a follow-up motor or a servo motor.

Included in our improved amplifier are means for permitting direct coupling of D.-C. amplifier stages which are A.-C. energized. This may be done by balancing out the fixed bias produced in the output of one stage to prevent its affecting the input of the next stage, and simultaneously providing a signal hold-over means, from one half-cycle of applied energy to the next halfcvcle. whereby successive stages may operate successfully despite opposite phase of energization.

Referring to the drawings,

Fi l is a perspective view of the pick-off or signal generating portion for a positional control device, such as used with a directional gyro or a gyro compass.

Fig. 2 is a similar View of a slightly modified form of signal generator.

Fig. 3 is a wiring diagram showing a modified -of gyroscope Ward Leonard servo system, and the rate amplifier therefor, controlled from the signal generator of Fig. 1 or Fig.2.

The pick-off means or signal generator is shown in Fig. l as a variable. inductive device comprising a three-legged transformer I mounted on a gear follow-up platform 2 which may be rotated from the follow-up motor 3. The center leg 4 of the transformer is shown as continuously excited from a single phase A. C. source 2,! while the two outer legs and ii are connected in opposition so that their output through lines 'i'- I is zero when the transformer is balanced, but is of one phase as the induced current in one leg predominates and of the other phase as the induced current predominates in the other leg. Cooperating with said transformer is shown a pair of soft iron armatures 8 and 9 which may be of nearly semi-circular form, each mounted on a common non-magnetic base is secured to vertical stem II rising from the vertical ring I2 of a gyroscope I4 through an aperture in platform or gear 2 and the hub I5 of the support for. transformer I, so that said armatures are fixedly oriented in azimuth from the gyroscope I l. The armature 8 is shown as of less diameter than armature 9 so that it passes between and above poles I and 6 while the armature 9 passes between and above poles 4 and 5. In the normal balanced condition, the two ends I3 and I3 of the armatures lie about on a line with the two outer edges of the poles d, 5, and 6, in which position there is no net output from the signal generator through lines 'l-l', since the voltages induced in legs 5 and 6 then balance one another. Preferably each pole piece is tapered, gradually increasing in cross-sectional area as it recedes from the tips it and I3, By this means, a signal which increases with angular displacement is secured through a fairly large displacement angle, as opposed to the prior art as indicated by the above cited patent. This form of inductive pick-01f also has the advantage that control is not lost except when the angular displacement approaches 90 either side of the balanced position, thus maintaining full control over 180 degrees of arc.

The output from this pick-off device, which is the voltage appearing across terminals 1-1, may be amplified in the rate amplifier shown in Fig. 3, which, as will be later described, introduces velocity and acceleration components into the control signal, which then may control motor 3 to drive follow-up platform 2 and transformer I into correspondence with armatures 8, 9, the system then acting as a follow-up system. The position of platform 2, which is thereby kept synchronized with that of base It and hence with gyroscope It, may be transmitted to a remote point as by Selsyn transmitter It, to give a suitable remote indication.

Alternatively, the output of the rate amplifier .may control any suitable remote motor, such as .241 (Fig. 3) to remotely control any suitable object, such as a rudder 225i. The system may thereby act as an automatic pilot, turning a craft until the orientation of platform 2, which would then be fixed to the craft, corresponds with that The craft then acts as the follow-up element of the system.

It will be obvious that the mountings of transformer I and armatures 3, 9 may be interchanged; that is, the transformer may be mounted on the gyro vertical ring it, and the armatures on the platform 2. v I

Also. armatures 8, e, instead of tapering from both ends to the center, might taper continuously from one end to the other. This would give full 360 degrees of control with continuously increasing signal.

In the form of invention shown in Fig. 2 the inductive transformer I is similar to that of Fig. 1 opt that the three poles in this instance are arranged circumferentially instead of radially as in 1. In this case, the center pole 4 is of greater width than the outer poles 5' and 6' and the gyro stabilized armatures 8 and 9 are shown as of uniform width. With this construction, armature 8 effectively cooperates only with poles i and ii, while armature 9 cooperates only with poles l and 5.

With this type of pickwff, a sharp increase in signal output is obtained for small displacements of armatures 8', 9' relative to transformer I, but -al does not vary with displacement over ice angle, as is the case with the device of Fig. 1. However, full control is maintained over ire 360 degrees of rotation.

Referring now to Fig. 3, the signal output from pick-of" unit I is fed to primary winding H33 of input transformer I by wires Iil'i. Transoer its has a center tapped secondary winding and two other similar secondary windings III H 3, Center tap H5 of winding 509 is connected to the cathodes E II, N9 of duplex tube I25 by way of cathode bias resistor W3 Whose resistance value selected so as to permit both sections of tube iii to operate at the center of linear portions of their characteristic curves. Tube I2! is as being a twin-tetrode having a pair of control grids i25, IE'I, a pair of additional grids Mi apair of anodes Q33, I35.

Control grids lit, 52? are connected to the outside terminals of secondary I69, thereby being energized in push-pull fashion. Anodes i33. I35 energized cophasally from a sources I31 of al -rnating current, which also supplies the pickoff unit IiiI, by way of conductor I39, output resistors i i-i, M3, and turned chokes i 15, I l-l, tuned to the frequency of the source 53?. The other terminal of source E3? is connected by wire M9 to center tap Hit of secondary winding Ids. Grids 529, i3i, which act as screen grids in the present illustration, are energized from sources I31 by way of a voltage dropping resistor I5I. Bypass condenserltt, i5-5, I51, I58 are also used.

In the absence of input voltage to grids I25, IN, the circuits of both sections of tube lZI are balanced, so that equal (and opposite) voltages will appear across output resistors Ml, Hi3.

In operation, the output of pickofi device lei will be an alternating voltage having the same or opposite phase with respect to that of source it'i. Phase adjuster I96, which may be a variable condenser, is adjusted to assure this proper phase relation. This phase adjuster may be inserted in lines 2i, if desired. The output voltage is fed in push-pull to the control grids I25, i2! by way of transformer 665. Hence, one of the two grids I25, it? will have an impressed voltage thereon of the same phase as its corresponding anode, and the other will have opposite phase, it being noted that both anodes 533, I 35 are energized in like phase from source iS'I. Which particular grid H5 or l2? has this same phase as its corresponding anode will depend on the phase of the output voltage from pickoff device NH, and will, therefore, depend on the sense of the relative motion between the armature ISI and field I63 of the pickofi device IilI. For purposes of illustration, let it be assumed that grid I25 has a voltage impressed on it in phase with its anode I33. Then, during the half-cycles of supply source I31 when anode I33 is positive with respect to cathode II1, the upper section of tube I3I will be more conductive than with zero voltage applied to grid I25, and an increased output voltage will appear across output resistor I4 I. During the other half-cycles, the conduction of this section of tube I2I will be blocked by its anode voltage, which is then negative with respect to cathode I H. The upper sec tion of tube I2I, therefore, acts as a half-wave rectifier. Tuned choke I45 and bypass condensers I53, I55 prevent the alternating component of the output voltage of tube I2I from appearing across output resistor IGI.

At the same time, in the illustrative example used, grid I21 will have a negative voltage applied to it during the positive anode half-cycle, so that the current in, and the voltage drop across, resistor Hi3 will decrease from the value with zero voltage on grid I21. The net change in direct voltage across resistors MI and I43 corresponds in magnitude to the magnitude or the alternating voltage output from pickoff device Iiii, and in sense to the phase of that voltage, and thereby to the relative deviation of the pickoff armature. Tube I2I, therefore, acts as a phase sensitive amplifier and half-.Wave rectifier for the signal voltage from the pickoff device I9 I Connected across output resistor I is a difierentiating circuit comprising condenser 1'65 and variable resistance I61. A similar diiierentiating circuit I69, I1! is connected across the other output resistor I43.

Since condenser I65 (or !69) will pass current only if the voltage applied from resistor M! (-or I43) is varying, it will be evident that this current corresponds to a rate of change, or time derivative, of the voltage output of tube I2 I, and therefore, of the voltage output of pickoii IEI. This rate current, flowing through resistor I61 (01' Hit) will produce a rate voltage, adjustable in magnitude by adjusting the resistance valueof resister I51 (or Hi). This rate voltage is applied to a similar differentiating circuit !13, I to produce a voltage across resistor I15 corresponding to acceleration; that is, the time derivative or rate of change of the rate voltage. In order that the voltage across resistor I15 may have a velocity component in addition to its acceleration voltage, variable resistor I19 is shunted across condenser H3, thereby permitting an adjustable com ponent of rate current to flow through resistor I15. A. similiar circuit E81, $83, 535 is placed in the lower section of the push-pull circuit. Adjusting resistor 161 (or I'll) will adjust the amount of rate voltage produced, and will, therefore, also adjust the acceleration voltage produced, since the second differentiating circuit I13, I15 (or I8I, I33) depends for its input on the voltage across resistor I51 (or I1I). Adjusting resistor I19 (or I65) adjusts the relative amounts of rate and acceleration components produced across resistor 115. This may be readily seen from the fact that with zero value for resistance I19, no differentiation is possible, and the output is velocity only. With infinite resistance value for I19, no velocity component transmitted, and the output is pure acceleration. Intermediate value of resistance, of course, provide varying relative amounts of rate and acceleration com ponents.

In each of these differentiating circuits, the resistance (I61, I15, I1I, I83) is made small in value compared to the reactance of its correspending capacitance (I65, I13, I69, I8I) at the low frequencies corresponding to the rates of variation of signal voltage magnitude, in order to provide efiective difierentiation. Also, the total impedance of the second difierentiating circuits (I13, E15 and I8I, I83) is made high compared to that of resistance I61 or I1I, in order to prevent undue loading of the first difierentiating circuits (I65, I61 and I69, I1I).

In the same manner as the second derivative or acceleration voltage is obtained, third, fourth or higher derivatives, as desired, may also be obtained.

The combined rate and acceleration voltage appearing across the resistance I15 (I83) is connected in series with a voltage representing the original signal or displacement voltage itself, obtained from secondary winding ill (or II3) by means of magnitude adjusting potentiometer I81 (or I89). Winding II I, in the illustrative example used, is connected so as to increase the current to anode 20I, while winding H3 is connected oppositely. The combined displacement, rate, and acceleration voltage is applied between cathode I9I (or I33) and control grid I (or I91) of tube I11, in series with cathode biasing resistor I99. Anodes WI, 263 of tube I11 are energized through their respective load resistors 265, 261 from source I31. It will be noted that one terminal of source I31 is already connected, by wire I39 and resistor I99 to cathodes I9I, I93. Hence, wire 2%! leading to anodes 26!, 263 is connected to the other side of supply source I31. Grids 2, M3 act as screen grids and are connected to wire 26!! by voltage dropping resistor 2I5.

Anode 2th is connected directly to control grid 2I9 of duplex tube 223, and similarly anode 203 is connected directly to grid 22!. Anodes ZUI and 2&3 are connected together by condenser 2 I1. The common terminal 225 is connected to cathodes 221, 229 by cathode biasing resistor RSI.

The anodes 233, 235 are energized from source i31 through their respective matched loads 231, 239 which form two similar and opposed field windings for direct current generator 24L These windings are bypassed by bypass condensers 243. 245. Since cathodes 221, 229 are directly connected to wire 299, anodes 233, 235 must be connected to the other terminal of source I31, as by conductor I39.

The field windings 231, 239 form highly inductive loads, which, when working out of low resistance driving sources, such as power amplifier tubes or gas-filled tubes, would have high time constants, preventing close following of the controlled motor. However, in the present system the generator fields are matched to the plate resistances of their respective amplifier tubes, and the combination is one inherently having a small time constant, permitting accurate control.

Tube I11 serves as a D.-C. amplifier for the combined displacement, rate and acceleration voltage connected to its control grids. Since this tube is energized by alternating current from source I31, it will conduct only during half cycles in which conductor 23 is positive with respect to cathodes I9I, I93. Hence, voltage will appear across its output resistor295 (or 2%?) only during these half-cycles. The circuits of both sections of tube i11 are also balanced, so that, with zero signal on both grids 85, i91, equal current will flow in, and equal voltage drops will appear across, output resistors 205, 231. Cathode biasing resistor I99 is selected in resistance value to pro- 7 vide operation about the center of the linear portion of the grid characteristic of each section of the tube I'll.

It will be seen that, during those half ,cycles when tube ill conducts, the total voltage drop across resistor M (or 1287) will bias grid Zia (or 22!), However, this will not 'afifect that output of tube 223, since during those same half-cycles, anodes 233, 235 are negative and tube 223 does not conduct. During the other half cycles, no grid voltage would appear on grids 2 l e, 22 l, as tube ET. is then non-conductive. To avoid this difficulty, condenser 25'! is connected across grids 259 and 22!, being also across output resistors 285, 231. With zero input to tube ill, condenser 2H is uncharged, since the stand-by or Zero input, voltage across resistor 295 balances and cancels that across resistor 28?, leaving zero net voltage across condenser 2H. When input voltage is applied to the grids I95, E9? of tube ill, the voltages across resistors 255, 28'! will change, and in opposite directions, during half-cycles when anodes Evil, 2% are positive. In the illustrative example used, the voltage across resistor 295 will increase, and that across 297 will decrease. The net change in voltage will charge condenser 2H, so that, during the succeeding half-cycles, when tube H1 is non-conductive, this net voltage will persist and be maintained on grids 2l9, EM, and will control tube 223, since anodes 235 are then positive. In this manner, the stand-by voltages across resistors 235, 29? have no effect on grids 2E9, 22!, only the changes in these voltages being used' in the succeeding stage. This arrangement provides a very successful directcoupled direct-current amplifier directly energized from a single source of alternating current, since the standby voltages have no effect on the succeeding stage.

Condenser 2i? may be made adjustable, and should be adjusted to give maximum output.

It is clear that the number of 31-0. amplifier stages may be extended as much as desired, merely assuring that each stage is energized from the A.-C. source in a phase relation opposite to that of the previous stage, and that some means, such as condenser 2, is used to enable holdover of the useful portion of the output voltage from the preceding stage, and to prevent the adverse biasing efiect of the standby voltage drops.

The output currents of tube 223 are smoothed by condensers 253 and 2 35 and energized field windings 237 and 239 of generator 24-5, which form the load on, and are matched in impedance to, the sections of tube 223. windings 237 and 239 are identical, and the sections of tube 223 are balanced so that equal currents will flow in windings 23?, 235 with zero input to tube 223. Tube is also operated at the center of the linear portion of the grid characteristic. Under these conditions the effects of the two windings 23?, 239 cancel one another. When input voltage is applied to the grids 2E8, 22! of tube 223, in the manner described above, the current through one Winding 237 or 239 will increase and that through the other will decrease, producing a net magnetic field whose magnitude and polarity correspond to the magnitude and polarity of the signal. Generator armature 2M is driven at constant speed by any suitable means, such as motor 242, and will generate a voltage also correspondto the combined signal. This generator output voltage is fed to the armature of direct current motor 2M, whose field 2459 has fixed excitation from a suitable direct current source.

The armature resistance of motor 241 is'matched to that of the generator 24!, including the effect of armature reaction, so as to provide maximum power transfer therebetween. Hence, motor 24'! will turn at a speed corresponding to the combined voltage and in a direction corresponding to the signal voltage phase. Motor fi l! may be directly coupled, as by pulley arrangement 248, to any type of load, such as rudder 25!, or followup device 2.

iubes l2i, ill and 223 have been illustrated as being of the duplex or twin type of tube. It is obvious that two separate tubes could be used in place of each of these twin tubes. Also, these tubes need not be tetrodes or triodes, as shown. It is immaterial whether they be triodes, tetrodes, pentodes or other types of tub-es, so long as they operate as linear amplifier tubes. Also, they may be of the vacuum or grid-controlled gas-filled type.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having described our invention, what we claim and desire to secure by Letters Patent is:

1. In a rate circuit comprising a source of first signal votage, a first difierentiating means for producing a second signal voltage corresponding to a time derivative of said first signal voltage, said diiierentiating means including an adjustable resistance element connected to provide said second signal voltage thereacross, a second differentiating means connected with said resistance element for producing from second signal voltage a third signal voltage corresponding to a time derivative of said second signal voltage, said second differentiating means including an element having resistance across which said third signal voltage is produced, and variable resistance means for supplying a component of said second signal voltage to said last mentioned element.

2. In a rate circuit comprising a source of first signal voltage, means for producing a second signal corresponding to a time derivative of said first signal, said means including a first variable resistor across Which said second signal is produced, and a network comprising parallel connected capacitance and a second variable resistor and an element having resistance connected in series with said parallel capacitance and resistor, said network being connected across said first variable resistor and said capacitance and said element having such capacitative and resistive values respectively as to function as a differentiating circuit, whereby to provide a signal output including said second signal and a third signal corresponding to a time derivative of said second signal.

3. A rate circuit having an input and an output, a source of first signal voltage connected across said input, a first difierentiating means for producing a second signal corresponding to a time derivative of said first signal, a second diilerentiating means for producing from said second signal a third signal corresponding to a time derivative thereof, said second differentiating means including an element having resistance connected to said output, said first differentiating means including an adjustable impedance means connected to provide said second signal voltage thereacross whereby to control the maximum value of said second and third signals for a given value of said first signal, and adjustable coupling means connecting said adjustable impedance with said output whereby to supply a component of said second signal to said output and to control the values of each of said second and third signals; whereby the magnitudes of said time derivative signals may be simultaneously adjusted to a limiting value and the relative values thereof as so limited may be simultaneously adjusted.

4. A rate'circuit comprising a source of first signal voltage, a first differentiating means for producing a second signal corresponding to a time derivative of said first signal, a second differentiating means for producing from said second signal a third signal corresponding to a time derivative thereof, said second differentiating means including a resistance element across which said third signal is produced, said first differentiating means including an adjustable impedance means connected to provide said second signal voltage thereacross whereby to control the maximum value of said second and third signals for a given value of said first signal, adjustable coupling means connecting said adjustable impedance with said resistance element of the second difierentiating means to control the values of each of said second and third signals and for supplying a component of said second signal to said resistance element; whereby the magnitudes of said time derivative signals may be simultaneously adjusted to a limiting value and the relative values thereof as so limited may be simultaneously adjusted, and means for combining with said second and third signals a component of said first signal.

5. A rate circuit comprising a source of first signal voltage, means for producing therefrom a second signal corresponding to a time derivative of said first signal and including a variable resistor across which said second signal is produced, a resistance-capacitance network connected across said variable resistor for producing from said second signal a third signal corresponding to a time derivative thereof, and variabie resistance means connected with said variable resistor and in shunt with said capacitance, said last-mentioned means serving to supply a component of said second signal to the output of said network and being so constructed and arranged as to differentially regulate the relative magnitudes of said derivative signals in the resultant signal.

6. In a rate circuit comprising an output and input adapted to receive a first signal voltage, a first differentiating means for producing a second signal corresponding to a time derivative of said first signal and including an adjustable resistance element across which said second signal is produced, a second differentiating means connected with said resistance element and with said output for producing a third signal corresponding to a time derivative of said second signal in said output, and variable impedance means connecting said adjustable resistance element with said output for supplying a component of said second signal to said output; said variable impedance means being adjustable simultaneously to regulate the values of each of said second and third signals and thereby to control the ratio thereof.

PERCY HALPERT. CARL A. FRISCHE. JOHN L. BIRD. ORLAND E. ESVAL.

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